1. Technical Field
The present invention relates to an oscillator, an electronic apparatus, and a moving object.
2. Related Art
JP-A-8-272463 (Patent Literature 1) describes a semiconductor integrated circuit (a semiconductor IC (Integrated Circuit)) in which an oscillation circuit and a logic circuit (a digital circuit) are respectively connected to individual voltage regulators and the oscillation circuit and the logic circuit operate at different power supply voltages.
When an oscillator including the semiconductor integrated circuit described in Patent Literature 1 is realized, since an amplitude level of an output signal of the oscillator generated by the logic circuit is determined by a standard (e.g., an amplitude level of approximately 2.8 V), for example, a relatively high power supply voltage of approximately 3.3 V is sometimes necessary as power supply voltages input to the regulators. When the oscillator is configured to be capable of receiving, from the outside, an input of a digital signal for controlling an oscillation frequency, the amplitude of the digital signal is set to 3.3 Vpp and the oscillator determines that, for example, with 1.65 V set as a threshold, the digital signal is at a high level if the digital signal is higher than 1.65 V and is at a low level if the digital signal is lower than 1.65 V.
On the other hand, recent process miniaturization is conspicuous. In a semiconductor integrated circuit manufactured by a fine process, an operating voltage is lower due to limitation of a withstanding voltage of a transistor. Since the semiconductor integrated circuit that controls the oscillator (the semiconductor integrated circuit that outputs the digital signal) has a large circuit size, high integration is necessary. Therefore, the semiconductor integrated circuit often operates at a low voltage such as 0.9 V or 1.2 V. Therefore, the semiconductor integrated circuit that controls the oscillator needs to convert the amplitude of a signal generated on the inside into 3.3 Vpp with a level shift circuit and output the digital signal. Then, power consumption of the semiconductor integrated circuit and the oscillator increases and noise received by the oscillator increases in proportion to a square of the amplitude of the input digital signal. On the other hand, it is also conceivable that, in the oscillator, a power supply voltage of a digital input section, to which the digital signal is input, is set to a fixed power supply voltage adjusted to the amplitude of the digital signal to make the level shift circuit unnecessary in the semiconductor integrated circuit that controls the oscillator. However, in the oscillator, the threshold for determining whether the input signal is high or low is fixed and an allowable range of a high level input is narrow. Therefore, it is difficult to enable connection of all of a plurality of kinds of semiconductor integrated circuits having different amplitudes of output signals. The oscillator is poor in versatility. That is, there has been a demand for an oscillator having a wider allowable range of a high level of a digital signal than in the past in order to satisfy versatility.